The present invention relates in general to the field of fluid-driven impellers, and in particular to those suitable for use in turbine flowmeters in which the axis of rotation is transverse to the direction of fluid flow.
Turbine flowmeters have a long established reputation for extremely accurate measurements of fluid flow rates, along with high rangeability, typically in the range of 10 to 1 or greater. In a turbine flowmeter the impact of a fluid stream on the blades of a turbine rotor produces rotation at a frequency proportional to the volumetric flow rate of the fluid. To date, the majority of turbine flowmeters used in industry are of the axial type, in which the axis of turbine rotation is generally parallel to the direction of fluid flow through a pipe or conduit. However, the benefits normally attributable to turbine flowmeters in general are offset by several significant drawbacks in the case of the axial type flowmeter. The size of the axial flowmeter rotor offers a substantial amount of blockage to fluid flow and creates a significant pressure drop, to reduce greatly the efficiency of fluid transfer through the pipeline. For larger pipeline diameters, the diameter of the turbine rotor correspondingly increases to span the larger distance. Typically the length of the flowmeter, i.e., in the direction of fluid flow, increases as well, due to hydrodynamic considerations, to allow for velocity profile conditioning of the fluid stream before it contacts the rotor blades. In other words, larger pipe size diameters generally require longer, more cumbersome and more costly turbine flowmeters.
The unavoidable presence of the rotor bearing surfaces within the potentially corrosive fluid stream means that elaborate fluid seals are needed to protect the bearings against premature deterioration. The presence of the bearings inside the conduit also precludes maintenance or replacement of the bearings without interrupting fluid flow and removing the flowmeter from the pipeline. All of the above disadvantage mean greater material and operating costs, so much so that for larger pipe sizes, such as twenty-four inches and larger, the cost of an axial turbine flowmeter makes their use impractical. Also, the extended length of the typical axial meter makes it difficult for it to be usable as a replacement for a narrow profile flowmetering installation, such as, for example, an orifice plate-differential pressure (d/p) cell combination.
For a variety of reasons, vertical axis turbine flowmeters, in which the rotor rotates about an axis oriented transversely to the flow of fluid, have not attained the degree of popularity enjoyed by axial flowmeters.
Earlier transverse axis flowmeter designs typically used a "squirrel-cage" type rotor or similar configurations in which multiple blades or rotor elements were distributed evenly about the central axis. Some designs included flow-diverting mechanisms to insure that fluid was being directed onto the rotor elements in such a way as to produce a continuous driving torque regardless of the orientation of the elements. Such arrangements were used probably because the viscosity of fluid typically causes considerable resistance to rotor movement, and unless the rotor were subjected continually to a driving force sufficient to overcome this resistance, it would reach a null position and stop rotating. These arrangements also make the rotor self-starting regardless of its initial orientation relative to the incoming fluid stream. However, such bulky rotor configurations unnecessarily add to the overall dimensions of the flowmeter, and so suffer from the same limitations as the axial-type meters, regarding replacement in a narrow profile installation.
Therefore it is an object of the present invention to achieve continuous flow-rate-proportional rotation of a vertically aligned flowmeter rotor element, in a minimum of longitudinal space.
It is a further object of the present invention to provide a turbine flowmeter capable of directly replacing an orifice plate within a pipeline.
It is yet another object of the invention to provide a turbine flowmeter which yields an accurate indication of average fluid flow within a pipeline without creating a significant pressure drop or loss of pumping efficiency.
It is another object of the invention to permit placement of turbine meter rotor bearings and rotation sensors outside of the fluid stream to facilitate maintenance and replacement thereof.
It is a further object of the invention to achieve the foregoing with a minimum of material and manufacturing costs.